1. Field of the Invention
The present invention relates to a steering system for a motorcycle and a motorcycle including the steering system.
2. Discussion of the Background
As a related art steering system for a motorcycle, there has been known the steering system in which the upper portions of front forks for rotatably supporting a front wheel are held by a top bridge, the top bridge is attached to a head pipe, and a steering handlebar is attached to the top bridge, thereby freely steering the front forks (for example, see JP Patent No. 2987221).
Now, typically in motorcycles, a top bridge holds a front fork at both ends thereof, and is supported by a head pipe at an intermediate portion thereof. Thus, when a front wheel runs over obstacles and the front forks are compressed, the top bridge is subjected to an upward bending moment around the head pipe, and in particular, stress is concentrated on root portions of holding portions for holding the front forks. Also, in the same manner as the front forks, a steering handlebar is attached to both ends of the top bridge. Therefore, when the steering handlebars are steered, the top bridge is subjected to a bending moment in a steering direction around the head pipe, and stress also tends to be concentrated on the root portions of the holding portions for holding the front forks.
Here, like the steering system for the motorcycle disclosed in JP Patent No. 2987221 as described above, when a top bridge is shaped like a simple plate, it is common practice to increase the thickness of the entire top bridge in order to ensure the rigidity of the top bridge against the above-described bending moment, or the like. In this case, it has been a problem that there is a limit to the reduction in weight of the top bridge.